Neurofilament protein distribution in the macaque monkey dorsolateral premotor cortex

Regional and laminar distribution patterns of neurofilament proteins in the dorsolateral premotor cortex (PMd) were studied with monoclonal antibody SMI-32 in five adult macaque monkeys and compared with the cytoarchitectonical features of the PMd. Our goal was to reveal whether the increasing functional diversity of the PMd which electrophysiological studies have unravelled over the last years is reflected on a structural level by differences in the neurochemical phenotype. Differences in size, shape and packing density of immunopositive layer III and V pyramidal cells define areas much more clearly than do differences in cytoarchitecture. The PMd can be subdivided into a rostral and a caudal part at a level slightly anterior to the genu of the arcuate sulcus. The extent of these two areas matches the two cytoarchitectonically defined areas F7 and F2, respectively. Within area F2, differences in layer V immunoreactive neurons define a dorsal (F2d) and a ventral (F2v) region. The border between areas F2d and F2v lies at the superior precentral dimple and cannot be detected cytoarchitectonically in Nissl-stained sections. Neurofilament proteins are involved in the stabilization of the cytoskeleton of the axon and have been correlated with axonal size and conduction velocity of nerve fibres. This regional variability in the neurochemical phenotype of layer V within the caudal PMd may reflect a differential organization of the descending output from this part of the premotor cortex. It might also be related to differences in the motor control of voluntary arm and leg movements.     

Distribution of cat-301 immunoreactivity in the frontal and parietal lobes of the macaque monkey

The distribution of the monoclonal antibody Cat-301 was examined in the frontal and parietal cortex of macaque monkeys. In both regions the distribution was uniform within cytoarchitecturally defined areas (or subareas) but varied between them. In all areas, Cat-301 labeled the soma and proximal dendrites of a restricted population of neurons. In the frontal lobe, Cat-301-positive neurons were intensely immunoreactive and present in large numbers in the motor cortex (area 4), premotor cortex (area 6, excluding its lower ventral part), the supplementary motor area (SMA), and the caudal prefrontal cortex (areas 8a, 8b and 45). In the parietal lobe, large numbers of intensely immunoreactive neurons were evident in the post-central gyrus (areas 1 and 2), the superior parietal lobule (PE/5), and the dorsal bank (PEa), fundus (IPd), and deep half of the ventral bank (POa(i] of the intraparietal sulcus (IPS). Two major patterns of laminar distribution were evident. In motor, supplementary motor, premotor (excluding the lower part of its ventral division), and the caudal prefrontal cortex (Walker's areas 8a, 8b and 45), and throughout the parietal cortex (with the exception of area 3), Cat-301-positive neurons were concentrated in the lower part of layer III and in layer V. The laminar positions of labeled cells in these areas were remarkably constant, as were the proportions of labeled neurons that had pyramidal and nonpyramidal morphologies (means of 30.2% and 69.8%, respectively). In contrast, in prefrontal areas 9, 10, 11, 12, 13, 14, and 46, in the cingulate cortex (areas 23, 24 and 25), and in the lower part of the ventral premotor cortex, Cat-301-positive neurons were spread diffusely across layers II to VI and a mean of 3.6% of the labeled neurons were pyramidal while 96.4% were nonpyramidal. Area 3 was unique among frontal and parietal areas, in that the labeled neurons in this area were concentrated in layers IV and VI. The areas in the frontal lobe which were heavily labeled are thought to be involved in the control of somatic (areas 4 and 6) and ocular (areas 8 and 45) movements. Those in parietal cortex may be classified as areas with somatosensory functions (1, 2, PE/5, and PEa) and areas which may participate in the analysis of visual motion (Pandya and Seltzer's IPd and POa(i), which contain Maunsell and Van Essen's VIP). The parietal somatosensory areas are connected to frontal areas with somatic motor functions, while POa(i) is interconnected with the frontal eye fields (8a and 45).(ABSTRACT TRUNCATED AT 250 WORDS)     

Development of non-phosphorylated neurofilament protein expression in neurones of the New World monkey dorsolateral frontal cortex

We studied developmental changes in the expression of non-phosphorylated neurofilament protein (NNF) (a marker of the structural maturation of pyramidal neurones) in the dorsolateral frontal cortex of marmoset monkeys, between embryonic day 130 and adulthood. Our focus was on cortical fields that send strong projections to extrastriate cortex, including the dorsal and ventral subdivisions of area 8A, area 46 and area 6d. For comparison, we also investigated the maturation of prefrontal area 9, which has few or no connections with visual areas. The timing of expression of NNF immunostaining in early life can be described as the result of the interaction of two developmental gradients. First, there is an anteroposterior gradient of maturation in the frontal lobe, whereby neurones in caudal areas express NNF earlier than those in rostral areas. Second, there is a laminar gradient, whereby the first NNF-immunoreactive neurones emerge in layer V, followed by those in progressively more superficial parts of layer III. Following a peak in density of NNF-immunopositive cell numbers in layer V at 2-3 months of age, there is a gradual decline towards adulthood. In contrast, the density of immunopositive cells in layer III continues to increase throughout the first postnatal year in area 6d and until late adolescence (> 1.5 years of age) in prefrontal areas. The present results support the view that the maturation of visual cognitive functions involves relatively late processes linked to structural changes in frontal cortical areas.     

Neuropeptides in cerebral cortex of macaque monkey (Macaca fuscata fuscata): Regional distribution and ontogeny

The concentrations of vasoactive intestinal polypeptide, somatostatin and substance P were determined in various cerebral subdivisions of adult and foetal Japanese monkeys (Macaca fuscata fuscata) by specific radioimmunoassays. In adult tissues, the highest level of vasoactive intestinal polypeptide was found in the somatosensory cortex and the lowest level in the occipital cortex. A high level of somatostatin was found in the association cortex (prefrontal, parietal and temporal cortex); the lowest level was noted in the occipital cortex. Substance P was found to be high in prefrontal and temporal cortex. The highest levels of substance P and somatostatin were obtained in the amygdala. Between embryonic 4 and 5.5 months, concentrations of peptides increased dramatically, and in the adult, all neuropeptides in cortical subdivisions significantly decreased. By the gel filtration method, only one immunoreactivity which coeluted with substance P and vasoactive intestinal polypeptide was demonstrated in extracts of 4-, 5.5-month-old and adult monkey cerebral cortex. In contrast, somatostatin immunoreactivity eluted as 3 peaks. Almost 80% of the immunoreactivity co-eluted with synthetic somatostatin, regardless of the age of the tissue. The molecular weights of two larger molecules were determined to be 13 and 3 kdaltons.     

Developmental changes in the relationship between type 2 synapses and spiny neurons in the monkey visual cortex

This study continues an exploration of synaptic development in the primary visual cortex of the monkey (Macaca nemestrina). In a prior study (Mates and Lund, '83a), we observed that type 2 synapses on the cell bodies of spiny stellate neurons of lamina 4C appeared not only to increase in number during early postnatal development but also subsequently decreased during maturation. Using quantitative, stereological electron microscopic methods, we examined the maturation of this synapse population from embryonic day 159 to adult, on spiny stellate neurons of 4C alpha and beta and, for comparison, on pyramidal neurons in upper and lower lamina 6. Tissue was also taken for comparison from two animals reared to 8 weeks of age with binocular eyelid closure from birth. We confirmed that a marked increase and subsequent decrease occurred in this somal type 2 synapse population on both neuron populations. However, due to the infrequency of the smooth dendritic neurons (approximately 5% of the neuron population) giving rise to the type 2 contacts, and due to expansion of the neuropil during maturation increasing intercell distances against constant volume of the type 2 axon arbors, it is concluded that the decrease in type 2 somal synapses may represent a redistribution to dendrites rather than loss from the neuropil. Cells of lamina 4C beta (receiving input from the parvocellular lateral geniculate nucleus-LGN) show a slower initial accumulation of type 2 contacts compared to neurons of lamina 4C alpha (receiving input from magnocellular LGN), or to pyramidal neurons of lamina 6.(ABSTRACT TRUNCATED AT 250 WORDS)     

Association fiber pathways to the frontal cortex from the superior temporal region in the rhesus monkey

The projections to the frontal cortex that originate from the various areas of the superior temporal region of the rhesus monkey were investigated with the autoradiographic technique. The results demonstrated that the rostral part of the superior temporal gyrus (areas Pro, Ts1, and Ts2) projects to the proisocortical areas of the orbital and medial frontal cortex, as well as to the nearby orbital areas 13, 12, and 11, and to medial areas 9, 10, and 14. These fibers travel to the frontal lobe as part of the uncinate fascicle. The middle part of the superior temporal gyrus (areas Ts3 and paAlt) projects predominantly to the lateral frontal cortex (areas 12, upper 46, and 9) and to the dorsal aspect of the medial frontal lobe (areas 9 and 10). Only a small number of these fibers terminated within the orbitofrontal cortex. The temporofrontal fibers originating from the middle part of the superior temporal gyrus occupy the lower portion of the extreme capsule and lie just dorsal to the fibers of the uncinate fascicle. The posterior part of the superior temporal gyrus projects to the lateral frontal cortex (area 46, dorsal area 8, and the rostralmost part of dorsal area 6). Some of the fibers from the posterior superior temporal gyrus run initially through the extreme capsule and then cross the claustrum as they ascend to enter the external capsule before continuing their course to the frontal lobe. A larger group of fibers curves round the caudalmost Sylvian fissure and travels to the frontal cortex occupying a position just above and medial to the upper branch of the circular sulcus. This latter pathway constitutes a part of the classically described arcuate fasciculus.     

Local circuit neurons of macaque monkey striate cortex: II. Neurons of laminae 5B and 6

This study investigates the intrinsic organization of axons and dendrites of aspinous, local circuit neurons of the macaque monkey visual striate cortex. These investigations use Golgi Rapid preparations of cortical tissue from monkey aged 3 weeks postnatal to adult. We have earlier (Lund, '87) described local circuit neurons found within laminae 5A and 4C; this present account is of neurons found in the infragranular laminae 5B and 6. Since the majority of such neurons are GABAergic and therefore believed to be inhibitory, their role in laminae 5B and 6, the principal sources of efferent projections to subcortical regions, is of considerable importance. We find laminae 5B and 6 to have in common at least one general class of local circuit neuron-the "basket" neuron. However, a major difference is seen in the axonal projections to the superficial layers made by these and other local circuit neurons in the two laminae; lamina 5B has local circuit neurons with principal rising axon projections to lamina 2/3A, areas whereas lamina 6 has local circuit neurons with principal rising axon projections to divisions of 4C, 4A, and 3B. These local circuit neuron axon projections mimic the different patterns of apical dendritic and recurrent axon projections of pyramidal neurons lying within laminae 5B and 6, which are linked together by both dendritic and axonal arbors of local circuit neurons in their neuropils extending between the two laminae. The border zone between 5B and 6 is a specialized region with its own variety of horizontally oriented local circuit neurons, and it also serves as a special focus for pericellular axon arrays from a particular variety of local circuit neuron lying within lamina 6. These pericellular axon "baskets" surround the somata and initial dendritic segments of the largest pyramidal neurons of layer 6, which are known to project both to cortical area MT (V5) and to the superior colliculus (Fries et al., '85). Many of the local circuit neurons of layer 5B send axon trunks into the white matter, and we therefore, suspect them of providing efferent projections. The axons of lamina 6 local circuit neurons have not been found to make such clear-cut contributions to the white matter.     

Local circuit neurons of macaque monkey striate cortex: I. Neurons of laminae 4C and 5A

A study has been made, using Golgi preparations, of the organization of neurons with smooth or sparsely spined dendrites, here called local circuit neurons, of the macaque monkey primary visual cortex. Since these neurons include those responsible for inhibitory circuitry of the cortex, a better understanding of their anatomical organization is essential to concepts of functional organization of the region. This account describes those neurons found with cell body and major dendritic spread within the thalamic recipient zone of lamina 4C and its border zone with lamina 5A. The neurons are grouped firstly in terms of in which laminar division the soma occurred--4C beta, 4C alpha or the border zone of 5A-4C beta--and secondly, into varieties on the basis of the interlaminar projection patterns of their axons. Most, if not all, of the local circuit neurons of these divisions have interlaminar axon projections as well as an arbor local to their cell body and dendritic field. These interlaminar projections are highly specific, targeting from one to five laminar divisions depending on the variety of neuron; on this basis 17 varieties of local circuit neuron are described. While the number of varieties appears dauntingly large in terms of understanding the functional circuitry of the region, the clear-cut organization of the interlaminar links may provide clues as to the information processing that concerns each neuron. The local circuit neuron axon projections can be related to a wealth of information already available concerning the laminar organization of afferent axons and efferent cell groups, the organization of spiny neuron intrinsic relays (presumed to be excitatory), and physiological properties of different laminar divisions. It is hoped that the information derived from this study can serve as a guide for correlated physiological-anatomical studies on single cells of the region.     

Cortical hierarchy reflected in the organization of intrinsic connections in macaque monkey visual cortex

Neuronal response properties vary markedly at increasing levels of the cortical hierarchy. At present it is unclear how these variations are reflected in the organization of the intrinsic cortical circuitry. Here we analyze patterns of intrinsic horizontal connections at different hierarchical levels in the visual cortex of the macaque monkey. The connections were studied in tangential sections of flattened cortices, which were injected with the anterograde tracer biocytin. We directly compared the organization of connections in four cortical areas representing four different levels in the cortical hierarchy. The areas were visual areas 1, 2, 4 and Brodman's area 7a (V1, V2, V4 and 7a, respectively). In all areas studied, injections labeled numerous horizontally coursing axons that formed dense halos around the injection sites. Further away, the fibers tended to form separate clusters. Many fibers could be traced along the way from the injection sites to the target clusters. At progressively higher order areas, there was a striking increase in the spread of intrinsic connections: from a measured distance of 2.1 mm in area V1 to 9.0 mm in area 7a. Average interpatch distance also increased from 0.61 mm in area V1 to 1.56 mm in area 7a. In contrast, patch size changed far less at higher order areas, from an average width of 230 m?M in area V1 to 310 m?m in area 7a. Analysis of synaptic bouton distribution along axons revealed that average interbouton distance remained constant at 6.4 m?m (median) in and out of the clusters and in the different cortical areas. Larger injections resulted in a marked increase in the number of labeled patches but only a minor increase in the spread of connections or in patch size. Thus, in line with the more global computational roles proposed for the higher order visual areas, the spread of intrinsic connections is increased with the hierarchy level. On the other hand, the clustered organization of the connections is preserved at higher order areas. These clusters may reflect the existence of cortical modules having blob-like dimensions throughout macaque monkey visual cortex. © 1993 Wiley-Liss, Inc.     

Distribution of parvalbumin-immunoreactive cells and fibers in the monkey temporal lobe: The amygdaloid complex

The calcium-binding protein parvalbumin was immunohistochemically localized in the monkey amygdaloid complex. Parvalbumin-immunoreactive neuronal cell bodies, fibers, and terminals were observed in several amygdaloid nuclei and cortical areas. Three types of aspiny neurons, ranging from small spherical cells (Type 1) to large multipolar cells (Type 2) and fusiform cells (Type 3) were observed in most amygdaloid regions, though the proportions of the cell types were different in each region. The density of parvalbumin-immunoreactive fibers and terminals tended to parallel the density of labeled cell bodies. The highest densities of parvalbumin profiles were observed in the nucleus of the lateral olfactory tract, the periamygdaloid cortex (PAC2), the magnocellular division of the basal nucleus, the ventrolateral portion of the lateral nucleus, and the accessory basal nucleus. The regions containing the lowest densities of parvalbumin-positive profiles were the medial nucleus, anterior cortical nucleus, central nucleus, and the paralaminar nucleus. In regions with fiber and terminal labeling, pericellular networks of fibers, reminiscent of basket cell terminations, were commonly observed to surround unstained neuronal cell bodies and proximal dendrites. In the magnocellular division of the basal nucleus, and to a lesser extent in the lateral nucleus, parvalbuminlabeled “cartridges” of axo-axonic terminals were observed on the initial segments of unlabeled cells. Parvalbumin-positive varicosities were also commonly observed in close apposition to the soma and dendrites of parvalbumin-immunoreactive cells. Given the close correspondence between the distribution of parvalbumin-positive neurons and a subset of GABAergic neurons in many brain regions, these data provide a first indication of the organization of the inhibitory circuitry of the primate amygdaloid complex. © 1993 Wiley-Liss, Inc.     

Corticopontine projections from the cingulate cortex in the rhesus monkey

The corticopontine projections of the cingulate cortices were investigated in the rhesus monkey with the use of autoradiography. A well-organized topography of projections was observed with anterior cingulate cortex projecting to the medial part of the pontine gray matter and posterior cingulate cortex projecting to the lateral part. Together these projections form a circle of termination around the periphery of the pontine gray matter.     

Cingulate cortex of the rhesus monkey: II. Cortical afferents

Cortical projections to subdivisions of the cingulate cortex in the rhesus monkey were analyzed with horseradish peroxidase and tritiated amino acid tracers. These projections were evaluated in terms of an expanded cytoarchitectural scheme in which areas 24 and 23 were divided into three ventrodorsal parts, i.e., areas 24a-c and 23a-c. Most cortical input to area 25 originated in the frontal lobe in lateral areas 46 and 9 and orbitofrontal areas 11 and 14. Area 25 also received afferents from cingulate areas 24b, 24c, and 23b, from rostral auditory association areas TS2 and TS3, from the subiculum and CA1 sector of the hippocampus, and from the lateral and accessory basal nuclei of the amygdala (LB and AB, respectively). Areas 24a and 24b received afferents from areas 25 and 23b of cingulate cortex, but most were from frontal and temporal cortices. These included the following areas: frontal areas 9, 11, 12, 13, and 46; temporal polar area TG as well as LB and AB; superior temporal sulcus area TPO; agranular insular cortex; posterior parahippocampal cortex including areas TF, TL, and TH and the subiculum. Autoradiographic cases indicated that area 24c received input from the insula, parietal areas PG and PGm, area TG of the temporal pole, and frontal areas 12 and 46. Additionally, caudal area 24 was the recipient of area PG input but not amygdalar afferents. It was also the primary site of areas TF, TL, and TH projections. The following projections were observed both to and within posterior cingulate cortex. Area 29a-c received inputs from area 46 of the frontal lobe and the subiculum and in turn it projected to area 30. Area 30 had afferents from the posterior parietal cortex (area Opt) and temporal area TF. Areas 23a and 23b received inputs mainly from frontal areas 46, 9, 11, and 14, parietal areas Opt and PGm, area TPO of superior temporal cortex, and areas TH, TL, and TF. Anterior cingulate areas 24a and 24b and posterior areas 29d and 30 projected to area 23. Finally, a rostromedial part of visual association area 19 also projected to area 23. The origin and termination of these connections were expressed in a number of different laminar patterns. Most corticocortical connections arose in layer III and to a lesser extent layer V, while others, e.g., those from the cortex of the superior temporal sulcus, had an equal density of cells in both layers III and V.(ABSTRACT TRUNCATED AT 400 WORDS)     

Local circuit neurons of macaque monkey striate cortex: III. Neurons of laminae 4B, 4A, and 3B.

We continue an investigation of the organization of local circuit neurons (largely inhibitory, GABAergic neurons, with smooth or sparsely spined dendrites) in the primary visual cortex of macaque monkey (Lund, '87: J. Comp. Neurol. 257:60-92; Lund et al., '88: J. Comp. Neurol. 276:1-29). This account covers local circuit neurons of layers 4B, 4A, and 3B; these three layers each receive different intrinsic second-order relays of principal thalamic inputs as well as receiving primary thalamic inputs in the case of two of the three laminae (4A and 3B). The study shows the existence of a number of different local circuit neurons making interlaminar projections between 4B, 4A, and 3B; each provides specific cross links between different combinations of the three laminae. It is known that the functional properties recorded physiologically from layers 4B, 4A, and 3B differ from one another and so these anatomical cross links may allow for correlation between different attributes of visual stimuli, e.g., color or motion, while still enabling separate processing of these different attributes to proceed in each of the three layers and be passed on to extrastriate areas. Whereas no spine-bearing neurons of layers 4B, 4A, or 3B provide "feedback" circuits to layer 4C (the source of their major intrinsic excitatory afferents), some of the local circuit neurons provide precisely structured axon feedback projections to divisions of 4C. The local circuit neurons also project to either lamina 5 or lamina 6, but not both and to superficial layers 3A, 2, and 1. Some local circuit neuron axon projections are of a dimension that would be confined to single functional clusters, e.g., cytochrome-rich "blobs," others reach out far enough to contact nearest neighbor "unlike" functional clusters, and yet others spread far enough to link repeating clusters of single function.     

Corticospinal projection patterns following unilateral section of the cervical spinal cord in the newborn and juvenile macaque monkey

Immediately following a unilateral section of the midcervical spinal cord that interrupts the dorsolateral, lateral, and ventral columns, the macaque monkey has a severe flaccid paralysis on the side of the lesion. Recovery of hand function is rapid, and, although it is incomplete, within a few months, the monkey uses the initially disabled hand and fingers with considerable skill. We examined the accompanying changes in the pattern of projection of corticospinal neurons to the cervical spinal cord that occurred following such a lesion. Spinal section was done both in newborn and juvenile macaques, and the postlesion period was followed for up to 150 weeks. Corticospinal neuron populations were visualized by using both anterogradely and retrogradely transported labels, and their origins, spinal pathways, and terminations were examined at intervals during the period of recovery of hand function. Immediately following unilateral section of the spinal cord at C3, sampled counts of soma profiles of retrogradely labeled neurons indicated that there was a profound reduction in the corticospinal projection to the hemicord caudal to the lesion. The few labeled corticospinal axons spared by the lesion bypassed the spinal lesion by descending in the contralateral cord and then crossing the midline caudal to the lesion. A few corticospinal axons may also have bypassed the lesion in the ipsilateral ventromedial column when this was not fully interrupted by the lesion. In every monkey, we observed a similar, profound reduction in the corticospinal (and rubrospinal) projections to the hemicord caudal to the lesion: This pattern did not alter significantly over an extended recovery period. An unchanging corticospinal projection to the cervical spinal cord contralateral to the lesion was also visualized in each monkey and resembled that seen in the normal macaque. Although the resolution of the labeling and counting procedures used precluded the identification of small increases in the numbers of corticospinal neurons projecting to the hemicord caudal to the lesion, we concluded that there was no substantial reconstruction of this projection over a recovery period of more than 2 years. J. Comp. Neurol. 381:282-306, 1997. © 1997 Wiley-Liss Inc.     

Postnatal development of thalamic recipient neurons in the monkey striate cortex: I. Comparison of spine acquisition and dendritic growth of layer 4C alpha and beta spiny stellate neurons

A quantitative study has been made from Golgi impregnations of the maturation of dendrites and their spines on spiny stellate neurons in the macaque monkey primary visual cortex. The neurons studied lay within either the alpha or the beta division of lamina 4C; previous workers have shown the alpha division neurons to be contacted by thalamic axon terminals arising from the magnocellular division of the lateral geniculate nucleus (LGN) of the thalamus and the beta division neurons to be contacted by parvocellular LGN inputs. Most thalamic terminals and perhaps the majority of other type 1 (Colonnier, '81), presumed excitatory, inputs to these cells make synaptic contacts on the tips of their dendritic spines. Measurement was made of relative changes in the total number of spines on these alpha and beta spiny neurons over age by measuring both spine density along the dendrites and dendritic arbor size in single 90-microns sections from Golgi rapid preparations. Our previous work (Lund et al., '77; Boothe et al., '79) showed a marked proliferation and attrition of spines and dendritic branches to occur in the early postnatal weeks; Rakic et al. ('86) have since proposed that there is a cortexwide synchrony of synapse acquisition and loss during this same period. However, different visual capacities channelled via the magnocellular and parvicellular geniculate relays show different maturational rates (Harwerth et al., '86). This study indicates that the anatomical maturation of spines on the alpha and beta neurons is not temporally coincident from birth to 30 weeks. During this period, phases of spine acquisition and loss on alpha neurons precedes similar phases on beta neurons. The alpha neurons carry a peak spine population at 5-8 weeks postnatal, whereas the beta neurons carry their peak spine populations between 8 and 24 weeks postnatal. At all ages prior to 30 weeks, the two sets of neurons carry quite different total spine populations. Close to 30 weeks of age, the total spine coverage has fallen on both sets of neurons and becomes identical between the alpha and beta neurons. In animals aged 30 weeks to adult, spine coverage per neuron is maintained at a common figure for the alpha and beta neurons despite further growth and disparate dendritic arbor sizes and different local spine densities in the two groups; this suggests that some common sampling paradigm between pre- and postsynaptic elements is adopted by the alpha and beta neurons and also suggests the development of a close functional correlation between the two sets of neurons.     

Subdivisions of auditory cortex and ipsilateral cortical connections of the parabelt auditory cortex in macaque monkeys

Auditory cortex of macaque monkeys can be divided into a core of primary or primary-like areas located on the lower bank of the lateral sulcus, a surrounding narrow belt of associated fields, and a parabelt region just lateral to the belt on the superior temporal gyrus. We determined patterns of ipsilateral cortical connections of the parabelt region by placing injections of four to seven distinguishable tracers in each of five monkeys. Results were related to architectonic subdivisions of auditory cortex in brain sections cut parallel to the surface of artificially flattened cortex (four cases) or cut in the coronal plane (one case). An auditory core was clearly apparent in these sections as a 16- to 20-mm rostrocaudally elongated oval, several millimeters from the lip of the sulcus, that stained darkly for parvalbumin, myelin, and acetylcholinesterase. These features were most pronounced caudally in the cortex assigned to auditory area I, only slightly reduced in the rostral area, and most reduced in the narrower rostral extension we define as the rostrotemporal area. A narrow band of cortex surrounding the core stained more moderately for parvalbumin, acetylcholinesterase, and myelin. Two regions of the caudal belt, the caudomedial area, and the mediolateral area, stained more darkly, especially for parvalbumin. Rostromedial and medial rostrotemporal, regions of the medial belt stained more lightly for parvalbumin than the caudomedial area or the lateral belt. The parabelt region stained less darkly than the core and belt fields. Injections confined to the parabelt region labeled few neurons in the core, but large numbers in parts of the belt, the parabelt, and adjacent portions of the temporal lobe. Injections that encroached on the belt labeled large numbers of neurons in the core and helped define the width of the belt. Caudal injections in the parabelt labeled caudal portions of the belt, rostral injections labeled rostral portions, and both caudal and rostral injections labeled neurons in the rostromedial area of the medial belt. These observations support the concept of dividing the auditory cortex into core, belt, and parabelt; provide evidence for including the rostral area in the core; suggest the existence of as many as seven or eight belt fields; provide evidence for at least two subdivisions of the parabelt; and identify regions of the temporal lobe involved in auditory processing. J. Comp. Neurol. 394:475–495, 1998. © 1998 Wiley-Liss, Inc.     

Corticospinal sprouting occurs selectively following dorsal rhizotomy in the macaque monkey

The corticospinal tract in the macaque and human forms the major descending pathway involved in volitional hand movements. Following a unilateral cervical dorsal root lesion, by which sensory input to the first three digits (D1–D3) is removed, monkeys are initially unable to perform a grasp retrieval task requiring sensory feedback. Over several months, however, they recover much of this capability. Past studies in our laboratory have identified a number of changes in the afferent circuitry that occur as function returns, but do changes to the efferent pathways also contribute to compensatory recovery? In this study we examined the role of the corticospinal tract in pathway reorganization following a unilateral cervical dorsal rhizotomy. Several months after animals received a lesion, the corticospinal pathways originating in the primary somatosensory and motor cortex were labeled, and terminal distribution patterns on the two sides of the cervical cord were compared. Tracers were injected only into the region of D1–D3 representation (identified electrophysiologically). We observed a strikingly different terminal labeling pattern post lesion for projections originating in the somatosensory versus motor cortex. The terminal territory from the somatosensory cortex was significantly smaller compared with the contralateral side (area mean = 0.30 vs. 0.55 mm²), indicating retraction or atrophy of terminals. In contrast, the terminal territory from the motor cortex did not shrink, and in three of four animals, aberrant terminal label was observed in the dorsal horn ipsilateral to the lesion, indicating sprouting. These differences suggest that cortical regions play a different role in post‐injury recovery. J. Comp. Neurol. 521:2359–2372, 2013. © 2012 Wiley Periodicals, Inc.     

Representation of face and intra-oral structures in area 3b of macaque monkey somatosensory cortex

Details of the representation of body regions innervated by the trigeminal nerve were elucidated in monkey cerebral cortex. Microelectrode recording was used to generate somatosensory maps in the posterior bank of the central sulcus and on the exposed cortical surface lateral to the lateral tip of the central sulcus in Macaca nemestrina. The area innervated by the contralateral trigeminal nerve is represented in an 8-mm mediolateral extent of area 3b lateral to the representation of the hand. Lateral to this, still within area 3b, there is an expanded representation of ipsilateral intra-oral structures measuring 6 mm in mediolateral extent. Both representations fill area 3b anteroposteriorly. The ipsilateral representation forms approximately 40% of the trigeminal representation, consistent with the amount of the ventroposterior medial (VPM) thalamic nucleus devoted to representation of ipsilateral intra-oral structures. Comparison of the present results with maps of the face representation in other species of monkey shows a consistent somatotopy of the face between species; size variations are mainly related to the enlarged ipsi- and contralateral representations of the cheek pouches in macaques. The general somatotopy of the trigeminal representation in monkeys is consistent with that in other mammalian species. © 1996 Wiley-Liss, Inc.     

Characteristics of the ipsilateral movement-related neuron in the motor cortex of the monkey

The characteristics of the precentral neuron activity related to ipsilateral movements were studied while the monkey was performing finger, wrist and arm movements on either side.Out of 197 task-related neurons, 134 discharged in association with contralateral movements, but not with any one of 3 ipsilateral movements. Fifty neurons discharged with bilateral movements.Thirteen neurons discharged in association with ipsilateral movements (ipsi-neurons). Ten were recorded from the trunk or shoulder area of the motor cortex and were accompanied by contraction of those muscles by intracortical stimulation (ICS). The remaining 3 were related to elbow or wrist, but no ipsi-neurons were related to finger muscle contractions.In ipsilateral task performance, 7 ipsi-neurons discharged in association with finger and/or wrist movements in addition to arm movement. Five others were associated with arm movement. The last one discharged with wrist movement. Most of the units showed similar response to contralateral movement.Ipsi-neurons were classified into two groups. One group was recorded around the sulcus precentralis superior, had the lower threshold current and was mostly associated with finger, wrist and arm movements. The other was recorded in the rostral motor cortex, and had the higher threshold current and was related to arm movement.Among 185 neurons to which pyramidal tract stimulation was delivered, 2 out of the 80 PTNs and 11 out of the 105 non-PTNs were ipsi-neurons.EMGs were recorded from various muscles involved in the forelimb movements. Arm and finger muscles showed no activity when the monkey used the ipsilateral hand, while most of the shoulder and trunk muscles showed tonic or moderate transient changes in the activity during the ipsilateral tasks. The ipsi-neuron activity was discussed in consideration with EMGs.